The invention relates to an in-line or on-line testing device used for analyzing the state of a chemical reaction. In a specific embodiment, the testing device is a rheometer.
1. Background of the Invention
Many chemical reactions are carried out in a continuous process, because of the efficiencies inherent in continuous processing related to yield and to eliminating the need to isolate intermediate products. In continuous chemical processing, it is sometimes important, in a multi-step chemical reaction, that the reaction reach a particular stage before parameters are changed, such as the addition of chemical compounds to the reaction, changes in temperature or atmospheric conditions, and the like. In the art, the status of the chemical reaction is often measured by removing a sample of material from the reaction process line, quenching the material, i.e. stopping the process of the chemical reaction, and analyzing the chemicals in the sample. The chemicals in the sample at that particular point define the status of the chemical reaction at that point, and tells the technician whether the reaction is proceeding as planned, and whether conditions are right for adding additional chemical reactants, or for changing the temperature or other parameters in the processing line.
A common means for determining the state of reaction of a process is to measure certain physical properties of the compound mixture which are a reflection of the nature of the material. Most chemicals, in a fluid state, exhibit rheological (flow) properties that are a function of the molecular size and structure of the material. For small chemical molecules with simple structure, the rheological properties of the material are fluid-like, independent of the rate and size of the applied deformation, and can be characterized in terms of a simple viscometric function such as a Newtonian viscosity. As molecular size and structure increases, a material""s rheological properties become more complex and are dependent on the size and rate of the applied deformation. Polymeric materials are comprised of very long molecules and exhibit viscous (fluid-like) as well as elastic (solid-like) behavior, known to those skilled in the art as viscoelasticity. Although characterizing the viscosity of a polymer can be descriptive of its molecular size, a viscoelastic characterization which is more sensitive to molecular structure is required since a viscometric function is not descriptive of the elastic nature of the material. A more thorough treatment for describing the molecular mechanisms underlying the viscoelastic rheological behavior of polymeric fluids can be found in xe2x80x9cViscoelastic Properties of Polymersxe2x80x9d by J. Ferry, Third Edition, John Wiley and Sons, New York (1980).
In the chemical processing art, it is a continuing goal to completely automate the processing line. By that, it is meant that if analysis of the chemical reaction stream can be made at critical points, and the data from those critical points is fed into a computer, the computer can use the information to know when to adjust the reaction conditions as necessary, to assure that the chemical reaction goes as planned, which will improve the efficiency and yield of the chemical process. The nature of the analyzing equipment used at the critical points depends on the nature of the chemical reaction and the kind of data that will be most useful in analyzing the status of the chemical reaction. Since a chemical processing line is sometimes used for preparing more than one kind of chemical, and the materials used in the chemical processing line will change depending on the reaction, it is desirable that the analyzing equipment used be useful for a broad spectrum of chemical reactions.
It is an object of the present invention to provide a method and apparatus for analyzing the chemical or physical properties of a fluid in a reaction flow stream.
Other objects of the invention will be apparent from the following description and claims.
2. Description of Prior Art
Various apparati have been developed for the use of on-line monitoring of a chemical process, most of which involve taking a side stream and pumping it through a capillary, slit, or rotating cylinder type of rheometer. These types of rheometers, however, typically provide only a viscometric and not a viscoelastic characterization of a fluid.
U.S. Pat. No. 4,468,953 (Garritano) describes an on-line concentric cylinder rotational rheometer for determining the vicoelastic properties of a fluid sampled from a process stream. The sampled fluid is introduced into the annular region of the concentric cylinders by means of a gear pump. The outer cylinder is made to oscillate about its axis of symmetry by means of a drive shaft and motor assembly, and the resultant torque on the inner cylinder is measured by means of a torsion tube assembly that is hermetically sealed. Flow into the rheometer is distributed uniformly through the annulus so that the introduction of fresh sample flushes the previous fluid sample out of the annulus. In order to allow free oscillation of the outer cylinder, however, the drive shaft requires the use of seals that are exposed to the thermal, chemical, and abrasive properties of the fluid. These seals require regular maintenance of the device and provide a possible source of failure during operation that could expose the surrounding environment to the hazards of the fluids being tested.
U.S. Pat. No. 4,643,020 (Heinz) describes a concentric cylinder process rheometer for characterizing the viscoleastic properties of a fluid that can be used either on-line or in the process stream. The sensing device consists of three concentric, thin-walled cylinders, the middle cylinder of which is made to oscillate about its axis of symmetry. The motion of the drive cylinder applies a shear to the fluid in the adjacent annular regions which causes a resultant torque on the drive cylinder that is measured on the drive shaft by means of a torsion tube and sensor assembly. Flexible bellows are used to seal the pivoting drive shaft from the fluid environment. Sample flushing out of the rheometer is uncontrolled, however, and the design does not allow for metered fluid flow into and out of the adjacent annuli to permit fresh sampling into the rheometer.
An apparatus for measuring the state of a chemical reaction in a process line comprises: (a) a cell of fixed volume for sampling and collecting material from a chemical process stream, and (b) a rheometer in which a portion of the sampled material is confined within a shearing gap where a controlled shear deformation is applied to the material and the response from the sheared material is measured.
In the illustrated embodiment, the rheometer cell is located external to the process stream, and material is allowed to enter and exit the cell by means of flow conduits and valves. The shearing gap is defined by the annulus of two substantially parallel concentric cylinder shafts. The inner cylinder moves axially in oscillation along its primary axis and is attached to a means of resolving (measuring) the physical material response to the applied deformation, in this case a force transducer.
Also provided is a method for measuring the flow response of fluids in a shear rheometer comprising the steps of, a) providing an apparatus for measuring the rate of shear flow of fluids comprising a drive shaft mounted external to the rheometer cell wherein the drive shaft is connected to a moving cylinder that defines the applied shear deformation, b) confining a portion of sampled material within the defined shear gap, c) causing the material confined within the defined gap to be sheared by the motion of the moving cylinder, and d) measuring the physical response created by the shearing of the sample.
An oscillating shear deformation is applied in order to assess the in-phase and out-of-phase physical responses to the applied deformation that are a reflection of the viscoelastic nature of a polymeric fluid. A step shear deformation may also be applied to the fluid in the gap, as in the case of a shear stress relaxation experiment. The shear deformation may also be applied such that the rate of fluid deformation in the shear gap is steady, as in the case of a viscometric flow characterization.
The rheometer provides a method for measuring the viscoelastic rheological properties of a fluid chemical that are a reflection of the state of chemical reaction of that chemical based on its molecular size and structure.
In an alternative embodiment, an apparatus 110 for inline testing of the properties of a fluid in a reaction flow stream comprises a container 122, consisting of container ends 122B, 122C and ring 122A connected to each other by bellows 120. An actuator shaft 124 within container 122 is connected to a shearing ring 126, the actuator shaft 124 being adapted to move shearing ring 126 within the container 122. A force transducer 128 is associated with the ring 122A for measuring torque forces on ring 122A.
The apparatus 110 has a shearing gap 116 which separates ring 122A and shearing ring 126 when shearing ring 126 is positioned within container 122 for obtaining test data. Shearing ring 126 has a cross-sectional shape which includes recirculation gaps 118. Apparatus 110 is adapted to be connected to a reaction flow stream by a tap line whereby a sample enters apparatus 110 through a first end 122B through portal 112, and exits apparatus 110 through portal 112A in second end 122C.